The 2011 Tohoku Tsunami observed by an array of ocean bottom electromagnetometers

Abstract

A tsunami induces secondary electromagnetic (EM) fields of significant intensity as a result of Faraday's law, and these EM fields can be recorded by instruments on the seafloor. Such observations will provide parameters that are useful in understanding tsunami generation and propagation processes. As such, EM sensors can be used as a type of tsunami sensor. In the present study, we report the observation of tsunami-induced EM signals by a small array of ocean bottom electromagnetometers consisting of four stations in the northwestern Pacific Ocean. Then, several data analysis methods are used to estimate tsunami parameters. Referring to the theoretical relation, the wave height is estimated from the observed magnetic and electric fields. Also, the propagation direction of the 2011 Tohoku Tsunami is estimated by applying analysis methods for an array and a single station.

Near‐ and far‐field tsunamigenic effects on the Z component of the geomagnetic field during the Japanese event, 2011

“…We associate these amplified pulses in Figure as dominantly of ionospheric current origin. For the CBI, this outcome is consistent with the finding of Zhang et al [] who noted the simulated disturbances of oceanic currents. Since their simulation did not include ionospheric dynamics, obviously, they will see only oceanic current contribution and any contribution from ionospheric currents.…”

“…Each panel displays the corresponding preprocessing magnetogram which was applied a high-pass filter with a cutoff period of 5000 s (Z component). The filter applied here was the same used by Zhang et al [2014] and also covers the spectral peak between 3 and 61 min detected by Kherani et al [2012]. The tsunami wavefield, obtained using the tsunami simulation model [Sladen et al, 2007;Sladen and Hébert, 2008], is also superimposed (black color) at each station in this plot.…”

“…Perturbations in the geomagnetic field induced by the tsunami have been observed by several authors [ Balasis and Mandea , ; Manoj et al , ; Toh et al , ; Utada et al , ; Klausner et al , ] and modeled [ Tyler , ; Kherani et al , ; Minami and Toh , ; Zhang et al , ; Kherani et al , ] in the previous literature.…”

“…Perturbations in the geomagnetic field induced by the tsunami have been observed by several authors [Balasis and Mandea, 2007;Manoj et al, 2011;Toh et al, 2011;Utada et al, 2011;Klausner et al, 2014] and modeled [Tyler, 2005;Kherani et al, 2012;Minami and Toh, 2013;Zhang et al, 2014;Kherani et al, 2016] in the previous literature. Manoj et al [2011] observed at three different observatories the geomagnetic disturbances caused by the tsunami of moderate level that occurred in the Pacific Ocean during February 2010 by the Chilean earthquake of magnitude 8.8.…”

Tsunami-induced magnetic fields detected at Chichijima Island before the arrival of the 2011 Tohoku earthquake tsunami

“…With the advancement of observational devices, tsunami-induced dynamo effects have recently been observed on the seafloor (Toh et al 2011;Ichihara et al 2013;Sugioka et al 2014;Zhang et al 2014a). A few instances of these effects have been documented on land.…”